Hello Jenna and Welcome to TE!

Many experts recommend a 10% increase per week maximum and every fourth week a 10% decrease (rest week). You are probably in very good shape already so maybe you can fit in more, but as you said, listen to your body. Besides your general health status, there's the fact that your position on the bike is not a usual one for your body and you must develop progressively the muscles to help you hold your body well in the saddle. I guess you should leave yourself some time to adapt...

Also remember to stock base miles (probably a few hundreds will suffice for you) before you start training hard on hills, intervals etc.